Heat applied electrochemical cell separator

ABSTRACT

A separator for a bobbin-style electrochemical cell is inserted into an interior opening within a ring-shaped cathode in an electrochemical cell can. An expansion force is then applied to an interior surface of the separator to press the separator against the interior walls of the cathode. A tool may then remove various creases and/or wrinkles in the separator and/or may then heat seal at least a portion of the tubular walls of the separator to minimize the void space between the separator and active material (e.g., cathode and/or anode) within the electrochemical cell.

BACKGROUND

Alkaline electrochemical cells are commercially available in cell sizescommonly known as LR6 (AA), LR03 (AAA), LR14 (C) and LR20 (D). The cellshave a cylindrical shape that must comply with the dimensional standardsthat are set by organizations such as the International ElectrotechnicalCommission. The electrochemical cells are utilized by consumers to powera wide range of electrical devices, for example, clocks, radios, toys,electronic games, film cameras generally including a flashbulb unit, aswell as digital cameras.

Battery manufacturers have made great strides to improve the capacity ofthe cells to improve the length of time that electrical devices can bepowered, while at the same time complying with the applicabledimensional standards for each cell size. As the shape and size of thebatteries are often fixed, battery manufacturers must modify cellcharacteristics to provide increased performance. For example, batterymanufacturers generally seek to maximize the total amount of activematerial, including both the positive electrode (cathode) material andnegative electrode (anode) material.

Due to consumers' increasing need for high-capacity electrochemicalcells offering maximal run-time, there is a constant need for improvedelectrochemical cell constructions offering improved dischargeperformance.

BRIEF SUMMARY

To provide increased electrochemical cell discharge performance, variousembodiments are directed to electrochemical cell constructionscomprising a hollow container housing a tubular cathode ring surroundingan interior of the hollow container. An electrochemical cell separatoris positioned within the hollow interior of the cathode, and iscompressed against the interior wall of the cathode to minimize thenumber of creases within the separator itself and/or to minimize thenumber of voids between the separator and the cathode. The separator maybe steamed in situ to further decrease the number of creases within theseparator itself and/or may be heat-sealed to prevent the positive andnegative active materials from coming in direct contact.

Certain embodiments are directed to a method for forming a separatorwithin an electrochemical cell. The method may comprise: providing acylindrical electrochemical cell can having an active material ringdisposed proximate an interior surface of the cell can; pressing aseparator into an opening within the active material ring; and applyingradial pressure to press the separator against interior walls of theactive material ring.

In various embodiments, the separator comprises separator comprises atleast two adjacent plies, and wherein the method further comprisesheating at least a portion of the separator to bond at least a portionof the adjacent plies together. Moreover, the separator may comprisesidewalls pressed against the interior walls of the active materialring, and a closed bottom end, and wherein the method may furthercomprise heating at least a portion of the sidewalls of the separator toheat seal adjacent plies of the sidewalls together.

The method may additionally comprise steps for forming a convoluteseparator by winding a separator sheet around a die; and whereinpressing the separator into the opening comprises pressing the convoluteseparator into the opening. In certain embodiments, the convoluteseparator has a tubular sidewall and a closed bottom end, and thetubular sidewall comprises at least one overlapping portion comprisingat least two adjacent layers of the separator sheet; and the methodfurther comprising steps for heating at least a part of the overlappingportion to heat seal the adjacent layers of the separator sheet.Moreover, the method may further comprise steps for heating at least aportion of the closed bottom end to heat seal the closed bottom end. Theseparator sheet of certain embodiments may be a nonwoven fibrousseparator sheet comprising thermoplastic fibers, and heating the atleast a part of the overlapping portion may melt at least a portion ofthe thermoplastic fibers. In certain embodiments, heating at least apart of the overlapping portion comprises applying an at leastsubstantially uniform heat to the interior surface of the separator.

In certain embodiments, the method further comprises steaming theseparator after pressing the separator into the opening. In variousembodiments, pressing the separator into the opening comprises pressingthe separator into the opening with a separator insertion tool; andexpanding the separator comprises inflating an expandable bladderdefining an exterior surface of the separator insertion tool to applyradial pressure the separator. In certain embodiments, inflating theexpandable bladder comprises providing a heated fluid to an interiorportion of the expandable bladder to apply heat to the separator.

Certain embodiments are directed to an electrochemical cell comprising:a container; a ring-shaped cathode disposed within the container whereinthe cathode defines an exterior surface in contact with the containerand an interior surface surrounding a hollow interior; an anode disposedwithin the hollow interior of the cathode; and a separator positionedbetween the cathode and the anode, wherein the separator has a tubularsidewall and a closed bottom end, wherein the tubular sidewall has atleast one overlapping portion defined by at least two layers of aseparator sheet being positioned between the cathode and the anode, andwherein at least part of the overlapping portions is heat sealed suchthat the at least two layers are bonded relative to one another.

In various embodiments, the separator is a nonwoven fibrous separator.Moreover, the nonwoven fibrous separator may comprise thermoplasticfibers and wherein portions of the thermoplastic fibers positionedwithin at least part of the overlapping portions may be melt-bondedrelative to one another. Moreover, the separator sheet may be ionpermeable and/or the overlapping portions of the separator sheet may beion permeable.

In certain embodiments, the separator is a convolute separatorcomprising a spirally wound separator sheet having a first end and asecond end, and wherein the first end overlaps the second end to formthe heat-sealed overlapping portion. Moreover, at least a portion of theclosed bottom end may be heat sealed. In certain embodiments, theseparator has an open top end opposite the closed bottom end, andwherein the heat sealed portion extends between the open top end and theclosed bottom end.

Certain embodiments are directed to a separator insertion tool forinserting a separator into a cylindrical electrochemical cell, theseparator insertion tool comprising: a body portion for pressing theseparator into the cylindrical electrochemical cell; and an expansionmember for selectably expanding the body portion to apply expansiveforces onto an interior surface of the separator.

In various embodiments, the body portion comprises a rigid cylindricalrod. Moreover, the expansion member comprises an inflatable bladdersurrounding the rigid cylindrical rod. In certain embodiments, theseparator insertion tool further comprises a fluid conduit extending atleast partially through the body portion, and the separator insertiontool may be configured to selectably expand the inflatable bladder bydirecting fluid through the fluid conduit and into the interior of theinflatable bladder. Moreover, the separator insertion tool may furthercomprise a heating element configured to heat seal at least a portion ofthe separator and/or at least one steam vent configured to emit steaminto the separator.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Reference will now be made to the accompanying drawings, which are notnecessarily drawn to scale, and wherein:

FIG. 1 is a cross-sectional view of a bobbin-style electrochemical cellaccording to one embodiment;

FIG. 2 is an exploded view of a bobbin-style electrochemical cellaccording to one embodiment;

FIGS. 3A-3B illustrate embodiments of a separator insertion tool inaccordance with the present description; and

FIGS. 4-5 illustrate additional example embodiments of a separatorinsertion tool in accordance with the present description.

DETAILED DESCRIPTION

The present disclosure more fully describes various embodiments withreference to the accompanying drawings. It should be understood thatsome, but not all embodiments are shown and described herein. Indeed,the embodiments may take many different forms, and accordingly thisdisclosure should not be construed as limited to the embodiments setforth herein. Rather, these embodiments are provided so that thisdisclosure will satisfy applicable legal requirements. Like numbersrefer to like elements throughout.

Electrochemical Cell

Referring now to FIG. 1, a bobbin-style electrochemical cell 10 is shownaccording to one embodiment of the present invention. In the illustratedembodiment of FIG. 1, the electrochemical cell is an alkaline cellhaving a manganese dioxide cathode active material and a zinc anodeactive material. However, it should be understood that theelectrochemical cell may have any of a number of active materialchemistries.

The alkaline electrochemical cell 10 shown in the exemplary embodimentand described herein is a cylindrical primary (non-rechargeable) batterycell of size LR6 (AA). However, it should be appreciated that theteachings of the present invention may be applicable to other alkalineelectrochemical cells of other shapes and sizes, including LR03 (AAA),LR14 (C) and LR20 (D) size cylindrical battery cells, as examples.Moreover, although the following specifically discusses cylindricalelectrochemical cells, it should be understood that various embodimentsare applicable for other cell shapes, such as rectangularelectrochemical cells, and/or the like. Additionally, theelectrochemical cell 10 may be employed as a single cell battery or maybe employed in a multiple cell battery.

The electrochemical cell 10 comprises a cylindrical container 12 thatmay be embodied as a metallic (e.g., steel) can, having a closed end 14,an open opposite end 16, and a cylindrical side wall extending betweenthe opposite ends. The cylindrical container 12 is made of a suitableelectrically conductive metal that may be formed into a desired shapeand is adapted to seal the internal contents within the cell 10. In theembodiment shown, the cylindrical container 12 also functions as thecathode current collector, and therefore exhibits good electricalconductivity. In one embodiment, the cylindrical container 12 may beplated with nickel and cobalt, such as may be achieved in an annealingprocess. The interior surface of the cylindrical container 12 may becoated with a graphite, if desired. In one example of an LR6 size cell,the cylindrical container 12 has a wall thickness of about 0.010 inch(10 mils or 0.025 cm) and the cylindrical wall has an outside diameterof about 0.548 inch (1.392 cm).

A positive contact terminal 30 comprising a plated steel or otherconductive metal material is welded or otherwise secured onto the closedend 14 of the cylindrical container 12 in the illustrated embodiment ofFIG. 1. However, in certain embodiments, the positive contact terminal30 may be integrally formed as a portion of the cylindrical container12. The positive contact terminal 30 has a protruding nubbin (i.e.,protrusion), at its center which serves as the positive contact terminalof the cell 10. Assembled onto the opposite open end 16 of thecylindrical container 12 is a collector and seal assembly made up of ananode current collector 34 (e.g., nail), a polymeric (e.g., nylon) seal26 and a negative contact terminal 32. The open end 16 of container 12is crimped onto the seal 26 which abuts bead 28 to seal closed the openend 16 of container 12. The negative contact terminal 32 forms anegative contact terminal of the cell 10. Positive and negative contactterminals 30 and 32 are made of electrically conductive metal and serveas the respective positive and negative electrical terminals.Additionally, a jacket 18 may be formed about the exterior surface ofthe cylindrical container 12, and may include an adhesive layer, such asa metalized, plastic film layer.

Disposed within the sealed volume of cylindrical container 12 is apositive electrode, referred to as the cathode ring 20, generallypositioned adjacent the interior surface of the cylindrical container12. The cathode has an exterior shape corresponding to the shape of thecontainer (e.g., the cathode positioned within cylindrical container 12has a generally cylindrical shape) with an interior surface defining aninterior cavity therein. For example, the interior cavity may have agenerally cylindrical shape, having an inside diameter ID. However, itshould be understood that the interior cavity may have any of a varietyof shapes. As other examples, the interior cavity may have a star-shape,an elliptical shape, a “gear” shape (having a plurality ofinterconnected cavities extending around a central hub, thus providingthe general shape of a gear), and/or the like. A separator 22 isdisposed in the interior cavity and contacts the interior surface of thecathode ring 20. A negative electrode, referred to as the anode 24, isdisposed within the interior cavity inside the separator 22.Additionally, an alkaline electrolyte solution, including water, isdisposed within the sealed volume of the container 12 in contact withboth the anode 24 and the cathode ring 20.

As discussed herein, the illustrated cathode ring 20 of FIG. 1 includesmanganese dioxide (MnO₂) as the electrochemically active material of thepositive electrode. Cathode ring 20 is generally formed of a mixture ofmanganese dioxide, graphite, barium sulfate, and aqueous alkalineelectrolyte solution. According to an impact molding embodiment, thecathode 20 may be formed by disposing a quantity of the cathode mixtureinto the open ended container 12 and, with use of an impact molding ram,molding the mixture into a solid tubular (e.g., cylindrical)configuration that defines a cavity generally concentric with the sidewall of the container 12. Alternately, according to a ring moldingembodiment, the cathode ring 20 may be formed by preforming a pluralityof rings (e.g., three or four rings) from the cathode mixture and theninserting the preformed rings into the container 12 to form the tubularshaped cathode ring 20. In certain embodiments, the interior surface ofthe cathode ring 20 (whether formed via impact molding or ring molding)may have a generally circular cross-section, a generally ellipticalcross-section, a generally “star”-shaped cross-section, and/or the like.

The anode 24, also referred to herein as the negative electrode, mayinclude a homogeneous mixture of an aqueous alkaline electrolyte, a zincpowder and a gelling agent, such as cross-linked polyacrylic acid. Thezinc powder is the electrochemically active material of the anode 24.The aqueous alkaline electrolyte may include an alkaline metalhydroxide, such as potassium hydroxide (KOH), sodium hydroxide ormixtures thereof. A gelling agent suitable for use in the anode 24 mayinclude a cross-linked polyacrylic acid, such as Carbopol 940®, which iscommercially available from Noveon, Inc., of Cleveland, Ohio. Examplesof other gelling agents that may be suitable for use in the cell 10 mayinclude Carboxymethyylcellulose, polyacrylamide and sodium polyacrylate.The zinc powder may include pure zinc or zinc alloy. Additional optionalcomponents of the anode 24 may include gassing inhibitors, organic orinorganic anti-corrosive agents, binders or surfactants that may beadded to the ingredients listed above. Examples of suitable gassinginhibitors or anti-corrosive agents include indium salts (such as indiumhydroxide), perfluoroalkyl ammonium salts, alkali metal sulfides, etc.Examples of suitable surfactants include polyethylene oxide,polyethylene, alkylethers, perfluoroalkyl compounds and the like. Theanode 24 may be manufactured by combining the ingredients into a ribbonblender or drum mixer and then working the anode mixture into a wetslurry.

In addition to the aqueous alkaline electrolyte absorbed by the gellingagent during the anode manufacturing process, an additional quantity ofaqueous solution containing a solution of potassium hydroxide and water,also referred to herein as free electrolyte, is added to theelectrochemical cell 10 during the manufacturing process. The freeelectrolyte may be incorporated into the cell 10 by disposing it intothe cavity defined by the cathode ring 20 after the separator 22 isinserted and may also be injected after the anode 24 is disposed intothe cell. According to one embodiment, the aqueous solution containsapproximately thirty-seven percent (37%) by weight KOH, and sixty-threepercent (63%) deionized water.

In the bobbin-type zinc/manganese dioxide alkaline cell 10 shown anddescribed herein, the separator 22 may be provided as a layered ionpermeable, non-woven fibrous fabric which separates the cathode ring 20from the anode 24. The separator 22 maintains a physical dielectricseparation of the cathode electrochemically active material (manganesedioxide) and the anode electrochemically active material (zinc) andallows for the transport of ions between the positive and negativeelectrode materials. Additionally, the separator 22 acts as a wickingmedium for the aqueous electrolyte solution and as a collar thatprevents fragmented portions of the anode 24 from contacting the top ofthe cathode ring 20. The separator 22 may include a conventionalnon-woven separator typically made of two or more layers of paper in theshape of a basket having a cylindrical wall and a closed bottom end.

The separator 22 comprises an ion permeable material having a highelectrical resistance (i.e., low electrical conductivity), such as athin nonwoven fabric. The separator may be a single-ply or multi-ply(e.g., two-ply) construction to provide a desired porosity to achievethe desired electrical resistance and ion-permeability while maintaininga low overall volume within an electrochemical cell. As mentioned above,because the overall volume of electrochemical cells are generally fixed,minimizing the overall volume of non-active materials (such as theseparator) within an electrochemical cell provides additional volumewithin the cell that may be occupied by electrochemical materials suchas the cathode and/or anode.

The nonwoven fabric of the separator 22 may be embodied as a fiber papercomprising natural, artificial, and/or synthetic fibers. For example,the fiber paper may comprise a blend of synthetic and artificial fibers,a blend of synthetic fibers and natural materials (e.g., wood pulp),and/or the like. As a specific example, the fiber paper may comprisefibrillated cellulose fibers and synthetic fibers. In certainembodiments, the synthetic fibers may comprise a thermoplastic material,such as polyvinyl alcohol fibers having a melting point of at leastabout 60° C., phenylboronic acid fibers (PBA fibers), and/or the like.In certain embodiments, the synthetic fibers may comprise firstsynthetic fibers that are soluble in water at a temperature of at least60° C. and second synthetic fibers that are insoluble in water.Moreover, the fiber paper may comprise solvent spun cellulose fiberssubject to fibrillation in well-known refinement and digestion processesin paper manufacturing.

The combination of the cellulose fibers and the synthetic fibers providea porous, non-woven fabric that may be rolled/coiled to form a tubularand/or convolute shape before or after being inserted into anelectrochemical cell 10. Moreover, the bottom end of the tubularseparator 22 may be folded to form a closed bottom end having a “cup”shape that may be inserted into an electrochemical cell. As yet anotherexample, the separator 22 may comprise a cross-strip separatorconstruction comprising two separator paper/fabric strips the centers ofwhich are overlapped and the strips are disposed at right angles suchthat the overlapped strips collectively have 4 at least substantiallyequal-sized portions extending at right angles relative to one anotherfrom a central hub portion. When inserted, each of the 4 portions isfolded upward toward the central portion to form an at leastsubstantially cylindrical shape with the hub portion defining the baseof the formed cylinder. Such an embodiment may form 4 overlappingportions as discussed in greater detail herein.

Once inserted into the electrochemical cell, the resulting separator 22defines an exterior surface surrounding the outside of the resultingseparator. The exterior of the sidewalls are in contact with an interiorsurface of the cathode, and the exterior bottom surface of the separatoris in contact with a portion of the can. As shown in the exploded viewof FIG. 2, the inserted convolute separator 22 defines one or moreoverlapping portions 23 in which at least two layers of separator paperare aligned to overlap one another within the electrochemical cell 10.In embodiments in which the separator 22 is defined as an at leastsubstantially continuous flat sheet of paper that is rolled to form theconvolute separator, the overlapping portions are located adjacentopposite ends of the continuous sheet of separator paper, and have alength (measured along the coiled length of the separator paper) equalto the portion of overlapping paper. Thus, the overall size of theoverlapping portions 23 are equal to the area of the thickest portion(measured in terms of greatest number of separator sheet layers) of theseparator 22. Moreover, the flat bottom end of the separator 22comprises overlapping portions to define a closed bottom end of theseparator 22.

In certain embodiments, one or more overlapping portions of theseparator 22 sidewalls and/or bottom end are heat sealed to at leastpartially secure overlapping portions of the separator relative to oneanother. As discussed in greater detail herein, the overlapping portionsof the separator 22 are heat sealed by applying a heat source (e.g., asteam filled chamber, a resistance heater, and/or the like) to at leastthe overlapping portions of the separator 22. The applied heat causes atleast a portion of the synthetic fibers within the separator paper tomelt and bond with portions of an overlapping portion of separator 22,thereby mechanically bonding the overlapping portions of the separator22. For example, a portion (e.g., a linear portion) of the separator 22sidewalls extending between an open upper end of the separator 22 and aclosed bottom end of the separator 22 may be heat sealed.

The resulting heat sealed separator 22 defines an at least substantiallycontinuous separator having a shape corresponding to the interiorsurface of the cathode ring 20 (e.g., a cylindrical separator shapecorresponding to a cylindrical cathode ring 20) without gaps betweenoverlapping portions of the separator 22. The heat sealed separator 22thus prevents undesirable movement of anode or cathode material betweensheets of the separator material that may cause internal short circuitswithin the electrochemical cell.

Moreover, in certain embodiments the separator 22 may be applieddirectly onto the interior surface of the cathode ring 20 once insertedinto the electrochemical cell 10. The separator 22 may thus be appliedto minimize the number and/or size of gaps between the interior surfaceof the cathode ring 20 and the exterior surface of the separator 22.Because each of those gaps occupy interior volume within theelectrochemical cell 10 that may otherwise be filled with activematerial, minimizing the number and/or volume of gaps between thecathode ring 20 and the separator 22 may provide an increased usableportion of the interior volume that may be utilized for active materialwithin the electrochemical cell 10.

In certain embodiments, radial pressure is applied to the separator 22utilizing an expandable insertion tool 100 as discussed in greaterdetail herein. The expandable insertion tool 100 may be configured topress (e.g., radially press) the separator 22 against the interiorsurface of the cathode ring 20. Moreover, the expandable insertion tool100 may be configured to apply steam to the separator 22 once insertedinto the electrochemical cell 10 to remove and/or minimize one or morecreases within the separator material.

In various embodiments, the insertion tool 100 may be configured toexpand and/or steam the separator paper prior to applying heat to heatseal portions of the sidewalls of the separator 22 to minimize gapsand/or creases between the separator 22 and the cathode ring 20 beforeheat sealing the separator 22. However, in certain embodiments theinsertion tool 100 may be configured to concurrently expand and pressthe separator 22 against the interior surface of the cathode ring 20 andto apply heat (e.g., dry heat or moist heat) to heat seal theoverlapping portions of the separator 22. In certain embodiments, theinsertion tool 100 may be configured to emit steam at a temperaturesufficient to simultaneously remove creases within the separator 22 andto heat seal overlapping portions 23 of the separator 22 relative to oneanother.

Separator Insertion Tool

Various embodiments are directed to an insertion tool 100 configured forinserting a separator 22 (e.g., a convolute separator, a cross-stripseparator, and/or the like) into an electrochemical cell 10 and forsmoothing the separator 22 along the interior wall of a cathode ring 20within an electrochemical cell 10. The insertion tool 100 may beembodied as an at least substantially cylindrical component that may beused to engage and insert an at least substantially cylindricalseparator 22 into an at least substantially cylindrical electrochemicalcell 10. In certain embodiments, the insertion tool 100 is configuredfor inserting a separator 22 into an irregular or otherwisenon-cylindrical cavity within a cathode ring 20. Accordingly, theinsertion tool 100 may have any of a variety of cross-sectional shapes,such as a shape corresponding to a shape of the cathode ring 20 interiorcavity.

FIGS. 3A-3B schematically illustrate one embodiment of a separatorinsertion tool 100. As shown in FIGS. 3A-3B, the separator insertiontool 100 may comprise an expansion component configured to expand adiameter D of the separator insertion tool 100 to provide radial forcesonto the interior surface of the separator 22. The expansion componentmay comprise an inflatable bladder 110 that may be selectively filledwith a fluid (e.g., air, heated air, steam, inert gas, heated inert gas,water, heated water, oil, heated oil, and/or the like) to expand thediameter D of the inflatable bladder 110.

The inflatable bladder 110 may surround a rigid insertion rod 120configured to press the separator 22 into the interior of theelectrochemical cell 10. The rigid insertion rod 120 may comprise ametal material (e.g., aluminum, steel, stainless steel, titanium, and/orthe like), a plastic material (e.g., a high-heat resistant plastic, athermoplastic, a thermoset plastic, and/or the like), a compositematerial, a ceramic material, and/or the like. In certain embodiments,rigid insertion rod 120 may comprise one or more fluid vents 121,valves, and/or the like configured to selectively enable fluid to beadded to the interior of the inflatable bladder 110. For example, theone or more fluid vents 121 may extend into an interior of the rigidinsertion rod 120 into fluid communication with a fluid conduit 113extending through an interior portion of the rigid insertion rod 120 toa fluid source (e.g., a pump, a compressed fluid storage container,and/or the like). As yet another example, the rigid insertion rod 120may be embodied as a porous rigid rod (e.g., comprising a plurality ofsintered particles collectively forming a rigid, porous rod that fluidmay flow through) defining a fluid conduit 113 through a central portionof the rigid rod 120.

In certain embodiments, the inflatable bladder 110 may comprise anelastic material having an at least substantially smooth surface. Forexample, the inflatable bladder 110 may comprise an elastic plasticmaterial configured to expand and stretch upon introduction of a fluid(e.g., a high-pressure fluid) within the interior of the inflatablebladder 110. In certain embodiments, the inflatable bladder 110comprises an elastic sack enclosing the one or more fluid vents 121,valves, and/or the like of the rigid insertion rod 120, and the elasticsack may have a closed end 111 and an open end 112. The open end 112 issecured with an airtight seal relative to a portion of the insertiontool at a seal member 122. The closed end 111 may extend around a rigidbottom portion of the rigid insertion rod 120. When in the unexpandedconfiguration, the inflatable bladder 110 may be form-fit around therigid insertion rod 120 of the separator insertion tool 100, such thatthe rigid insertion rod 120 of the separator insertion tool 100 may beutilized to form the cylindrical separator 22 (e.g., by wrapping planarseparator paper around the rigid insertion rod 120) and to initiallyguide the separator 22 into the electrochemical cell 10. Once theseparator 22 is placed within the electrochemical cell 10, theinflatable bladder 110 may be inflated such that the bladder expandsaway from the rigid insertion rod 120 in the separator 22 to applyradial pressure onto the separator 22 to press the separator against theinterior walls of the cathode ring 22. The inflatable bladder 110 mayexpand and contour to the interior surface of the cathode ring 20,thereby forming the separator 22 against the cathode ring 20. Thus, ifthe cathode ring 20 has an irregular interior surface, the inflatablebladder 110 may press the separator 22 against the irregular interiorsurface to conform the separator 22 to the shape of the cathode ring 20.As a specific example, the separator 22 and the inflatable bladder 110may expand within an interior opening of the cathode ring 20 having agear-shaped cross-section (as described herein) such that the separator22 is pressed into the plurality of interconnected cavities such thatthe separator 22 takes on a gear shaped cross-section conforming to theshape of the interior surface of the cathode ring 20. For example, apump mechanism in fluid communication with the interior of theinflatable bladder 110 via the fluid conduit 113 and one or more fluidvents 120 may be configured to pump fluid into the interior of theinflatable bladder 110 until the bladder reaches a defined pressure topress a separator 22 formed around the rigid insertion rod 110 againstthe interior walls of a cathode ring 20. Moreover, the pump may bereversible in certain embodiments, to deflate the inflatable bladder 110such that the separator insertion tool 100 may be easily removed fromthe interior of the electrochemical cell after the separator 22 ispositioned against the interior walls of the cathode ring 20. In certainembodiments, the inflatable bladder 110 may comprise one or more vents,holes, valves, and/or the like to allow fluid (e.g., air, steam, and/orthe like) to exit through the inflatable bladder 110 into theelectrochemical cell 10.

In certain embodiments, the inflatable bladder 110 may expand laterally,with the bottom portion (e.g., closed end 111) of the inflatable bladder110 secured relative to the rigid insertion rod 120 of the insertiontool 100 to press the sidewall of the separator 22 against the interiorsidewall of the cathode ring 20. However in certain embodiments theclosed bottom portion 111 of the inflatable bladder 110 may beconfigured to expand away from the rigid insertion rod 120 of theinsertion tool 100 to depress the closed bottom end of the convoluteseparator 22 against the closed bottom end of the electrochemical cell10.

In various embodiments, the inflatable bladder 110 may comprise anelastic plastic material having a high melting point, such that hightemperature fluids may be utilized to inflate the inflatable bladder110. In such embodiments, the elastic material of the inflatable bladder110 may also be a heat conductive material (or an inefficient heatinsulator) such that heat from the heated fluid may be transferred(e.g., via conductive and/or convective heat transfer) from theinflatable bladder 110 to the separator 22. As discussed herein, theinsertion tool 100 may be configured to apply sufficient heat to theseparator material to heat-seal overlapping portions of the separator22. Accordingly, the fluid within the inflatable bladder 110 may besufficiently hot that the inflatable bladder 110 may heat seal theseparator 22 upon compressing the inflatable bladder 110 against theinterior surface of the separator 22. In embodiments in which the fluidutilized to expand the inflatable bladder 110 is utilized to heat sealthe separator 22, the separator insertion tool 100 may be configured toapply an at least substantially uniform heat across at leastsubstantially the entirety of the interior surface of the separator 22sidewall.

In certain embodiments, the expansion mechanism may be embodied as oneor more panels 150 that may expand outward from a rigid portion 120 ofthe insertion tool 100. Each of the panels 150 may be at least partiallyrigid, and each may be configured to expand outward via a mechanicalmechanism (e.g., a hydraulic or pneumatic mechanism, a mechanicallinkage, and/or the like) to apply an outward, radial pressure onto theseparator 22 to press the separator 22 against the interior surface ofthe cathode ring 20. In certain embodiments, the insertion tool 100 maycomprise a plurality of expandable panels 150 (e.g., 2 panels, 3 panels,4 panels, 6 panels, 8 panels, and/or the like) to provide a generallyuniform pressure onto the separator 22.

Moreover, the insertion tool may comprise one or more heat sealmechanisms 160, such as a resistance heater wire, that may be configuredto apply (e.g., conduct) heat directly to the separator 22 to heat sealthe separator 22. The heat seal mechanism 160 may be provided oninsertion tools 100 with or without one or more expansion mechanisms,such that the heat seal mechanism 160 is configured to heat seal theseparator 22 once the separator 22 is in its final position within theelectrochemical cell 10. The heat seal mechanism 160 may be configuredfor near-instantaneous heat sealing, gradual heat sealing, and/or thelike. The heat seal mechanism 160 may be further configured to seal atleast a portion of the tubular sidewall of the separator and/or at leasta portion of the closed bottom end of the separator 22.

The heat seal mechanism 160 may extend along at least a portion of thelength of the separator insertion tool 100 to heat seal at least aportion of the separator 22 sidewall. For example, the heat sealmechanism 160 may extend at least substantially linearly along at leasta portion of the length of the separator insertion tool 100 to form aheat seal along at least substantially the entire height of theseparator 22, extending between an open upper end of the separator 22 tothe closed bottom end of the separator 22.

The insertion tool 100 may additionally comprise one or more steamnozzles 170 configured to apply steam to the separator 22 to at leastpartially heat and/or moisten the separator 22 to promote bondingbetween overlapping portions of the separator 22 when positioned withinthe electrochemical cell 10. In certain embodiments, the steam nozzles170 may be configured to apply steam to the separator 22 prior toapplying heat and pressure to press the separator 22 against the cathodering 20. The combination of heat and moisture applied to the separator22 may cause the one or more synthetic materials within the separator 22to dissolve and, upon drying, plasticize to heat seal adjacent portionsof the separator 22.

Method of Manufacture

Manufacturing of an electrochemical cell 10 according to variousembodiments begins by providing a cylindrical container 12 having anopen top end and a closed bottom end. In certain embodiments, the closedbottom end may define a protrusion (e.g., in the form of a plate weldedonto the closed bottom end or a protrusion integrally formed with thecylindrical container 12 itself. Active materials are then added to theinterior of the cylindrical container 12 through the open top end.Cathode material is first added to the cylindrical container 12 to forma cathode ring 20 adjacent the outer wall of the cylindrical container12. As noted above, the cathode material may be premolded into cathoderings, and one or more cathode rings may be added into the interior ofthe cylindrical container 12. Alternatively, granular cathode materialmay be added to the interior of the cylindrical container 12, and amolding ram may be inserted into the interior of the cylindricalcontainer 12 to impact mold the cathode material into a continuouscathode ring 20.

Once the cathode ring is positioned within the interior of thecylindrical container 12, the cathode ring 20 has an exterior surfaceadjacent the interior surface of the cylindrical container 12 wall andan interior surface defining an opening (e.g., a cylindrical opening) atleast substantially within the center of the cylindrical container 12.The separator 22 may then be placed within the opening within theinterior of the cathode ring 22. In certain embodiments, the separator22 may be formed of an at least substantially continuous rectangularpaper sheet that is coiled around an at least substantially cylindricalinsertion tool 100 to form a convolute separator 22. The coiled papersheet may form a single-layer ring having a short overlapping portionwhere portions proximate opposing ends of the paper sheet overlap toform an overlapping portion 23 comprising a two-layer portion. Incertain embodiments, the coiled paper sheet may form a multi-layer ring(e.g., at least two layers) having an overlapping portion where portionsproximate opposing ends of the paper sheet overlap to form anoverlapping portion 23 comprising at least one additional layer (e.g.,at least three layers where the convolute separator 22 comprises atleast two layers). A bottom end of the resulting convolute separator 22is folded inward over an end of the insertion tool to form a closedbottom end of the convolute separator 22.

It should be understood that the separator 22 may be formed by foldingand/or rolling paper in a variety of ways to provide a separator 22having a closed bottom end. In certain embodiments, the separator 22 maycomprise a plurality of overlapping portions. For example, a separatormay be a cross-strip separator comprising one or more separator papersheets folded over an end of an insertion tool 100 (e.g., in a “U”shape), and the portions of the separator paper sheet located onopposite sides of the insertion tool 100 may be folded toward oneanother, around the cylindrical insertion tool 100 to form a cylindricalseparator 22. In such an embodiment, the cylindrical separator 22 hastwo overlapping portions 23 on opposite sides of the resultingcylindrical separator 22.

Once the cylindrical separator 22 is formed around the insertion tool100, the insertion tool 100 pushes the separator into the interior ofcathode ring 20. Upon initial insertion, the combination of theinsertion tool 100 and the separator 22 have a diameter smaller than theinternal diameter of the cathode ring 20, such that the separator 22 maybe inserted into the cylindrical cell 10 without substantiallydisturbing the cathode ring 20. Once the separator 22 is at leastpartially inserted into the cell 10, the insertion tool 100 may expandto press the separator 22 against the interior walls of the cathode ring20 to conform the separator 22 to the shape of the interior surface ofthe cathode ring 20. As noted herein, the insertion tool 100 maycomprise an expansion mechanism such as an inflatable bladder 110surrounding an exterior of the insertion tool 100 that may be inflatedto apply a radial pressure to push the separator 22 against the interiorwalls of the cathode ring 20. The inflatable bladder 110 may be inflatedwith a fluid, such as a gaseous composition (e.g., air, heated air,steam, inert gas, a vapor, and/or the like) or a liquid composition(e.g., water, heated water, oil, heated oil, and/or the like). In otherembodiments, the insertion tool 100 may comprise one or moremechanically actuated expansion panels 150 that may be actuated viapistons, mechanical linkages, and/or the like within the interior of theinsertion tool 100.

The expansion mechanism is configured to press the separator 22 againstthe interior walls of the cathode ring 20 to minimize and/or eliminatevoids existing between the cathode ring 20 and the separator 22.Moreover, the insertion tool 100 may comprise one or more heatingmechanisms 160 and/or steam mechanisms to eliminate creases and/or otherimperfections within the separator 22 while positioned within thecathode ring 20. In various embodiments, the insertion tool 100 maycomprise one or more steam nozzles 170 configured to apply steam to theseparator 22 while positioned within the cathode ring 20. Theapplication of steam directly to the separator 22 may cause the removalof one or more creases, wrinkles, and/or the like within the separator22 to provide an at least substantially smooth separator 22 having an atleast substantially smooth shape corresponding to the shape of theinterior surface of the cathode ring 20.

Moreover, the insertion tool 100 may be configured to apply heat to atleast a portion of the separator 22 to heat seal at least theoverlapping portions of the separator 22. As noted above, the insertiontool 100 may comprise an inflatable bladder 110 that may be filled witha heated fluid, such as steam, heated water, and/or heated oil. Theheated fluid within the inflatable bladder 100 may apply heat to theseparator 22 sufficient to melt at least a portion of the syntheticfibers within the separator paper to heat seal layers of the separator22 relative to one another. However, it should be noted that theinsertion tool 100 may comprise separate heating elements 160 (e.g.,resistance heaters) configured to directly apply heat to the overlappingportions of the separator 22 (e.g., overlapping portions within thewalls of the separator and/or overlapping portions in the closed bottomend of the separator).

Once the separator 22 is placed within the cathode ring 20, theinsertion tool 100 may be removed from the cathode ring 20, leaving theseparator 22 behind. Particularly in those embodiments in which theinsertion tool 100 comprises one or more expansion configurations, theinsertion tool 100 may reduce its diameter (e.g., by reducing thediameter of the expansion configuration) such that the outer diameter Dof the insertion tool 100 is not in direct contact with the interiorsurface of the convolute separator 22. The insertion tool 100 may thenbe removed from the electrochemical cell 10, leaving an interior portionof the separator 22 open for the placement of anode material therein.

After removal of the insertion tool 100, anode material may be added tothe remaining opening within the interior of the separator 22, and freeelectrolyte may be added to the interior of the electrochemical cell 10.Because the separator insertion tool 100 caused removal of substantiallyall wrinkles and/or creases within the separator 22, the added anodematerial may form an anode component 24 having a sidewall shapecorresponding to the shape of the interior surface of the separator 22(and corresponding to the interior shape of the cathode ring 20). Theanode material may be a gelled anode material that may be extruded orotherwise added to the interior of the separator 22. Thereafter, theanode 24, current collector 34, and seal arrangement 32 are put in placeto seal the open end of the container 12 and to form a completeelectrochemical cell 10. Again, because the separator 22 is providedsubstantially free of creases and/or wrinkles, the useful volumeoccupied by active material, including both cathode and anode material,is maximized within the interior of the electrochemical cell 10.

Conclusion

Many modifications and other embodiments will come to mind to oneskilled in the art to which this disclosure pertains having the benefitof the teachings presented in the foregoing descriptions and theassociated drawings. Therefore, it is to be understood that thedisclosure is not to be limited to the specific embodiments disclosedand that modifications and other embodiments are intended to be includedwithin the scope of the appended claims. Although specific terms areemployed herein, they are used in a generic and descriptive sense onlyand not for purposes of limitation.

That which is claimed:
 1. A method for forming a separator within anelectrochemical cell, the method comprising: providing a cylindricalelectrochemical cell can having an active material ring disposedproximate an interior surface of the cell can; pressing a separator intoan opening within the active material ring; and applying radial pressureto press the separator against interior walls of the active materialring.
 2. The method of claim 1, wherein the separator comprises at leasttwo adjacent plies, and wherein the method further comprises heating atleast a portion of the separator to bond at least a portion of theadjacent plies together.
 3. The method of claim 2, wherein the separatorcomprises sidewalls pressed against the interior walls of the activematerial ring, and a closed bottom end, and wherein the method furthercomprises heating at least a portion of the sidewalls of the separatorto heat seal adjacent plies of the sidewalls together.
 4. The method ofclaim 1, further comprising forming the separator as a convoluteseparator by winding a separator sheet around a die; and pressing theconvolute separator into the opening after the winding.
 5. The method ofclaim 4, wherein the convolute separator has a tubular sidewall and aclosed bottom end, and the tubular sidewall comprises at least oneoverlapping portion comprising at least two adjacent layers of theseparator sheet; and the method further comprising heating at least apart of the overlapping portion to heat seal the adjacent layers of theseparator sheet.
 6. The method of claim 5, further comprising heating atleast a portion of the closed bottom end to heat seal the closed bottomend.
 7. The method of claim 5, wherein the separator sheet is a nonwovenfibrous separator sheet comprising thermoplastic fibers, and whereinheating the at least a part of the overlapping portion melts at least aportion of the thermoplastic fibers.
 8. The method of claim 5, whereinheating the at least a part of the overlapping portion comprisesapplying an at least substantially uniform heat to an interior surfaceof the separator.
 9. The method of claim 1, further comprising applyingsteam to the separator after pressing the separator into the opening.10. The method of claim 1, wherein pressing the separator into theopening comprises pressing the separator into the opening with aseparator insertion tool; and wherein applying radial pressure to theseparator comprises inflating an expandable bladder portion of theseparator insertion tool against the separator.
 11. The method of claim10, wherein inflating the expandable bladder comprises providing aheated fluid to an interior portion of the expandable bladder to applyheat to the separator.
 12. An electrochemical cell comprising: acontainer; a ring-shaped cathode disposed within the container whereinthe cathode includes an exterior surface in contact with the containerand an interior surface surrounding a hollow interior; an anode disposedwithin the hollow interior of the cathode; and a separator positionedbetween the cathode and the anode, wherein the separator has a tubularsidewall and a closed bottom end, wherein the tubular sidewall has atleast one overlapping portion defined by at least two layers of aseparator sheet being positioned between the cathode and the anode, andwherein at least part of the overlapping portion is heat sealed suchthat the at least two layers are bonded relative to one another.
 13. Theelectrochemical cell of claim 12, wherein the separator is a nonwovenfibrous separator.
 14. The electrochemical cell of claim 13, wherein thenonwoven fibrous separator comprises thermoplastic fibers and whereinportions of the thermoplastic fibers positioned within at least part ofthe overlapping portions are melt-bonded relative to one another. 15.The electrochemical cell of claim 12, wherein the separator sheet is ionpermeable.
 16. The electrochemical cell of claim 15, wherein theoverlapping portions of the separator sheet are ion permeable.
 17. Theelectrochemical cell of claim 12, wherein the separator is a convoluteseparator comprising a spirally wound separator sheet and having a firstend and a second end, and wherein the first end overlaps the second endto form an overlapping portion.
 18. The electrochemical cell of claim12, wherein at least a portion of the closed bottom end is heat sealed.19. The electrochemical cell of claim 12, wherein the separator has anopen top opposite the closed bottom end, and wherein the heat sealextends between the open top and the closed bottom end.